In general terms, this invention relates to timing circuitry which is able to accomplish analog integration as well as timing functions in any electronic system requiring highly accurate integrating and timing circuits.
More specifically, this invention relates to electronic timing circuitry which can be preset to some desired voltage-time integral, and which can in turn integrate a voltage proportional to a measured system parameter, such as velocity, and provide an output signal when the time integral of the parameter voltage is equivalent to the preset voltage-time integral.
The timing circuit integrates an input signal with respect to time, in an operational amplifier integrator, and when the integral, or time-volt product, is equal to a previously set-in (preset) product the output changes state. It can be used, for example, with an input voltage representing velocity to indicate when a certain preset distance has been covered; or with an acceleration to indicate when a desired velocity has been reached. The timing circuit is designed to give the greatest possible accuracy in the comparison of the integral of the preset and input signals. These two signals are both input on the same line, which makes the comparison independent of the input scaling resistor. The presaturation signal also utilizes the same input. A presaturation signal is sometimes called an initialization signal. Although the circuit operates in three modes, no actual switching is required within the circuit. As is shown in FIG. 1A, the three modes are (1) initialization or presaturation; (2) set-in; and (3) readout. This feature plus the method of very accurately clamping the integrator output, both in the plus and in the minus directions, makes this circuit unique.
A circuit to accomplish the same task has been developed in the prior art. It is described in U.S. Pat. No. 3,836,791, to Glenn L. Galloway, entitled PRESETTABLE SINGLE-INPUT VOLTAGE-TIME INTEGRATOR, which issued on Sept. 17, 1974. The timer described therein had the disadvantage that several of the component values and offsets in the circuit could affect its accuracy, whereas in this invention only changes in component values and offsets between preset and time out can affect accuracy. An offset voltage may be defined as "the difference in voltage at the two inputs of an operational amplifier required to bring the output voltage to zero". Other offset parameters can be defined in a similar manner.